| Supercapacitors with excellent power capacity,good safety performance and long cycle life are attracting wide attention as one of the energy storage devices.The main challenge for supercapacitors is to develop supercapacitors that have a high energy density similar to that of current rechargeable batteries while maintaining their inherent characteristics of high power density and long cycle life.Therefore,a great deal of research has been devoted to maximizing the specific capacitance or increasing the voltage to improve the performance of supercapacitors.In this paper,nitrogen-doped hollow carbon spheres were used as the substrate to prepare binary or ternary composites by combining with polyaniline,manganese dioxide or nickel-cobalt sulfide,so as to obtain supercapacitor electrode materials with high specific capacitance.Their capacitive properties were studied in acidic or alkaline solutions and the he main contents are as follows:(1)The Si O2spheres prepared by St?ber method were used as hard templates and dopamine hydrochloride as nitrogen source and carbon source to synthesize the nitrogen-doped hollow carbon sphere(NHCS)by self-polymerization,high-temperature carbonization,HF etching and other steps.Subsequently,a layer of polyaniline(PANI)was deposited on the surface of the nitrogen-doped hollow carbon spheres by chemical oxidation polymerization to form the double-hulled structure of NHCS/PANI binary composite.The materials were characterized by SEM,TEM and X-ray diffraction.The results showed that the shell thickness of the nitrogen-doped hollow carbon sphere was only 10 nm and the diameter was about 270 nm.After the successful deposition of polyaniline,the shell thickness increased to 20 nm.The electrode material was tested by cyclic voltammetry,galvanostatic charge/discharge and electrochemical impedance spectroscopy.The conductivity and specific capacitance of NHCS/PANI binary composites were higher than that of NHCS,but the specific capacitance only increased from 50 F·g-1to 93 F·g-1at the current density of 0.5A·g-1,with no significant increase.(2)The NHCS/Mn O2-30?NHCS/Mn O2-35 and NHCS/Mn O2-40 composites loaded with Mn O2particles on NHCS were obtained by the hydrothermal reaction of the nitrogen-doped hollow carbon spheres prepared above and potassium permanganate at different concentrations,and then polyaniline layers were deposited on these three materials to obtain NHCS/Mn O2/PANI-30,NHCS/Mn O2/PANI-35 and NHCS/Mn O2/PANI-40 ternary composites.Through characterization,it was found that almost all the NHCS in NHCS/Mn O2-40 were damaged,and the NHCS in NHCS/Mn O2-30 were the most intact,but there were few Mn O2particles deposited on the sphere.Only NHCS/Mn O2-35 maintained a good spherical structure and was loaded with more Mn O2particles.The presence of Mn O2particles enhanced the mechanical strength of NHCS,making the structure of NHCS/Mn O2/PANI-35 more complete than that of NHCS/Mn O2/PANI-30 in the materials after the deposition of polyaniline.The test results show that NHCS/Mn O2/PANI-35 in the prepared materials has the highest specific capacitance value,reaching 484 F·g-1at 0.5 A·g-1,which is significantly larger than that of NHCS/Mn O2-35 and NHCS/PANI.It shows that there is a good synergistic effect among the components of the ternary material.(3)The NHCS/Ni2Co1S4-1 composite was prepared by adding the prepared NHCS in the process of hydrothermal synthesis.The Ni2Co S4crystals in the material is the same as the pure Ni2Co S4,with serious accumulation and agglomeration,while NHCS-1 was dispersed on the surface and in the gaps of the aggregate.At the current density of 0.5 A·g-1,the specific capacitance of NHCS/Ni2Co1S4-1 was 1067 F·g-1,not much different from the 1020F·g-1of pure Ni2Co S4.Taking advantage of the difference between the pellet-forming speed of Si O2and the self-polymerization speed of dopamine hydrochloride in solution,the N-doped hollow carbon sphere precursor PDA@Si O2was prepared in one step,and then the NHCS-2 was prepared by high-temperature carbonization and etching processes.The nickel-cobalt sulfide was then grown on the surface of NHCS-2 by hydrothermal synthesis.The characterization results showed that the prepared nitrogen-doped hollow carbon spheres had a diameter of about 700 nm and a shell thickness of 30 nm,and almost all the spheres had mesoporous or macroporous not greater than 120 nm in their surfaces.The presence of these holes provides a channel for ions to enter the interior of the NHCS-2 sphere,so Ni2Co S4grows on both the inner and outer surfaces of the NHCS-2.In addition,the presence of NHCS-2 significantly weakens the agglomeration phenomenon of Ni2Co S4,which presents the characteristics of the scattered growth of a single cube crystal.Cyclic voltammetry,galvanostatic charge/discharge,electrochemical impedance spectroscopy and other tests were carried out on the prepared materials.The results showed that the specific capacitance of NHCS/Ni2Co S4-2 was up to 1468 F·g-1at the current density of 0.5 A·g-1,which was significantly higher than that of pure Ni2Co S4.After 1000 cycles of charging and discharging,the NHCS/Ni2Co S4-2 electrode shows good cyclic stability and its specific capacitance value can still remain at 87.4%of the initial specific capacitance value. |
PDF Full Text Request